1. Field of the Invention
The present general inventive concept relates to a projection-type image display apparatus that uses a light emitting diode (LED) light source, and more particularly, to a projection-type image display apparatus including a compact optical arrangement.
2. Description of the Related Art
In general, projection-type image display apparatuses provide an image by projecting an image formed on a display device onto a screen using light emitted from a light source. To realize compact projection-type image display apparatuses with a wide screen, a light emitting diode (LED) is used as the light source. If the LED is used as the light source, an illumination system can be made compact and a natural color image can be easily obtained because of the characteristics of the LED. Further, the LED has greater durability than a lamp that produces light through an arc discharge, and can operate at low power.
The LED produces a low light output. In the projection-type image display apparatuses with a wide screen, a plurality of LEDs should be used as light sources. An illumination system that emits light from the plurality of LEDs to a projection lens system typically requires a large configuration, thereby making it difficult to achieve a compact design.
Referring to FIG. 1, a conventional projection-type image display apparatus includes an illumination optical system 10 emitting a beam of a predetermined color, a glass rod 20 mixing incident light and making the incident light uniform, a display device 31 producing an image, a reflecting mirror 35 reflecting light emitted from the illumination optical system 10 to be directed toward the display device 31, and a projection optical system 40 projecting the image produced by the display device 31 onto a screen 50.
The illumination optical system 10 includes first through third LED light sources 11, 12, and 13, respectively, emitting blue light, red light, and green light. The illumination optical system 10 further includes first and second dichroic mirrors 15 and 16 disposed between the first and second LED light sources 11 and 12 and between the second and third LED light sources 12 and 13, respectively. The first and second dichroic mirrors 15 and 16 combine the blue light, red light, and green light to propagate along the same path, and a condensing lens 17 condenses the incident light.
The glass rod 20 includes an entrance surface 21 and an exit surface 25 through which light enters and exits, respectively. The glass rod 20 has a rectangular shape having a length between the entrance surface 21 and the exit surface 25 that is greater than a diagonal length of the entrance surface 21. As illustrated in FIG. 1, the glass rod 20 is longitudinally disposed along an incident light axis in a width direction (i.e., a horizontal direction when seen from FIG. 1) of the conventional projection-type image forming apparatus.
The projection optical system 40 is disposed on an emitted light axis to enlarge and project an incident image. As illustrated in FIG. 1, the incident light axis on which the glass rod 20 is disposed and the emitted light axis on which the projection optical system 40 is disposed intersect each other at a right angle.
Since the glass rod 20 is longitudinally disposed along the incident light axis, a space occupied by the glass rod 20 is large. Consequently, the projection-type image display apparatus constructed as above has a limitation in reducing its entire width.